1. Field of the Invention
The invention in general relates to the field of capacitive sensors for sensing the wall thickness of an object and more particularly relates to such a sensor that is useful in sensing the wall thickness of glass containers.
2. Description of the Prior Art
Capacitive sensors for sensing the wall thickness of objects such as glass bottles, flat glass and other products are well known. See for example U.S. Pat. No. 4,820,972 issued on an invention of Paul F. Scott et al and the various references cited therein. Such sensors generally include an electrode covered with protective layer of material which is non-abrasive and exhibits low wear in sliding contact with glass. The types of materials that are suitable for such tapes are limited because they must also provide an appropriate capacitance to permit the sensor to function. In the prior art, adhesive tapes made of ultra-high molecular weight polyethylene with a pressure sensitive rubber-based adhesive coating have provided such protective layers. Polyvinyl fluoride tapes with rubber-based adhesive coatings have also been suggested.